The present invention relates to a method of recording and reading optical information. More specifically, the present invention relates to the use of the photochiroptical effect in the recording and reading of optical information. The present invention also relates to a novel optical information medium for use in the method of recording and reading optical information.
A wide variety of means exists for the writing and retrieval of optical information. All of these methods involve a change in the optical characteristics of certain portions of an information layer during the writing process, with those changes being noted during the reading process. The use of an isomerization process for effecting the change in optical characteristics has been suggested, as has the switching of the optical storage material in the information layer to a plurality of oxidation states. This latter process has a potential of providing a ternary storage system.
For example, U.S. Pat. No. 4,663,270 issued to Potember et al, discloses a multistate organic optical storage medium wherein an optical beam can switch any data storage spot into three or more memory states. The storage medium consists of a mixture of bistate switching modules, or of large delocalized amphoteric molecules. The illuminated area of the optical storage medium undergoes an electrochemical topatic redox reaction thereby causing certain moieties in the illuminated area to change oxidation state. By changing the intensity of the optical "write" beam the illuminated area can be switched to a plurality of specific states with each state having a unique set of oxidation species. A ternary system can thereby be theoretically realized.
The use of isomerization as a technique in recording information in an optical medium is disclosed, for example, in U.S. Pat. No. 4,678,736 issued to Hanamura et al. The information bits are recorded by applying energy to a polydiacetylene thin film supported by a substrate, so that the main chain structure of the polydiacetylene is transformed into another form or forms. The changes are, more specifically, from the A-type bonding to the B-type bonding, and additionally from a planar configuration to a non-planer configuration. This change in form also results in a change of optical characteristics, which permits one to read the information recorded.
U.S. Pat. No. 4,686,169 issued to Yoshino et al relates to an optical disk structure in which an information layer of a photochromic dye is irradiated by laser light in order to record information. The photochromic dye exhibits the photochromizum based on a cis-trans isomerization. Such photochromic compounds include the amphipathic derivative of azobenzene, indigo or thioindigo. The dyes are stable in both the cis and trans forms, and the recorded information bit is read based upon the different light absorption spectra resulting from the two different forms.
The search continues, however, for improved systems in the recording and retrieval of optical information. The need for increased storage capacity, as well as improvements in the areas of error detection and correction, are necessary in order to provide a commercially viable system. To provide such a system is an object of the present information.
Other objects of the present invention will become apparent upon a review of the following specification and the claims appended hereto.